Recent proliferation of IEEE 802.11 WLANs (Wireless local area networks) stems from its attractive features such as low chipset cost, ease of deployment, and sufficient bandwidth. As IEEE 802.11 WLANs becomes a dominant wireless access technology, it requires more efficient use of scarce wireless resources.
Distributed Coordination Function (DCF), the most popular MAC protocol for IEEE 802.11 WLANs, is very simple and its distributed operations show good performance in most environment. DCF which is based on CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) prohibits concurrent transmissions in order to avoid packet collisions and harmful interferences.
However, this basic collision protection scheme (CSMA/CA) may not fully utilize the wireless resources in terms of spatial reuse due to its conservative medium access control. If we adjust the transmission order and relative signal strength, we can successfully transmit multiple packets without the collision and channel error. We call this Capture Effect.
Previous wireless NICs (Network Interface Card) enables the PHY capture when an intended signal arrives until the middle of the preamble time of an interference signal. Of course, the SINR (Signal to Interference plus Noise Ratio) value of the intended signal must satisfy the required capture threshold. Recent MIM (Message in Message)-capable NICs such as Athelos increases the PHY capture probability by using enhanced preamble detection functionality. MIM-capable NICs can capture the intended signal with higher SINR (≈10 dB) even if the intended signal arrives after the preamble time of an interference signal.
This is shown in FIG. 1. FIG. 1A shows PHY capture, and FIG. 1B shows MIM, respectively.
As shown in FIG. 1A, when an intended signal having high SINR of approximately 10 dB arrives within the preamble time of an interference signal, the intended signal can be captured.
With MIM function, an intended signal can be captured even though it arrives after the preamble time of an interference signal, as shown in FIG. 1B.
U.S. Pat. No. 5,987,033 is the related art for maximizing the PHY capture using MIM function. In U.S. Pat. No. 5,987,033, there are disclosed a receiver and a method for operating the receiver, for a station in a wireless local area network using a common wireless communication channel and employing a CSMA/CA protocol includes various modes. In normal mode, the receiver follows typical states in order to detect a message and demodulate data from the message properly. Meanwhile, a process implements a message-in-message (MIM) mode when an energy increase above a specified level is detected. While in the MIM mode, if a carrier is detected, the energy increase is caused by a new message; otherwise, the energy increase is caused by an interfering station. If the carrier is detected, the receiver begins retraining so that it can start receiving the new message as soon as the first message ends.